The counterfeiting of articles of many kinds is a serious worldwide problem, causing great loss of revenues to legitimate business, individuals, and governments. One approach to protect articles from counterfeiting is the incorporation of special markings that are difficult to reproduce but that enable easy detection. Examples are articles that are tagged or marked with identification marks that are printed using normally invisible chemicals, such as ultraviolet- or infrared-sensitive chemicals. Counterfeiters, however, have produced articles with similar hidden identification marks that are so sophisticated that only high performance scanners and laboratory equipment can distinguish the counterfeit article from the genuine article.
Many devices have been proposed to automatically determine authenticity of articles by detecting markings made with substances that are not normally visible in ordinary light, but become detectable by the devices when illuminated with non-visible radiation. One previous approach describes a label verification system in which each label to be verified is imaged onto a matrix of photocells, and an authentic label is imaged onto another matrix of photocells. Symbols on the labels preferably contain photoluminescent substances, and the matrix of photocells is provided with suitable filters, so that when the labels are illuminated with ultraviolet light, photocell responses are at a much higher degree of contrast.
Another approach discloses paper secured against forgery and a device for checking the authenticity of such papers. The paper carries materials that fluoresce in the visible, ultraviolet, or infrared spectral range in characteristic emission spectra. The device includes a light source for exciting fluorescent substances, a condenser lens concentrating the light emitted by the paper, a narrow band interference filter, a focusing lens, and a series of photocells arranged in the focal plane of the focusing lens. The outputs of the photocells are fed to a preamplifier and then to a comparator, and outputs of photocells are compared to establish the authenticity of the paper.
In still another approach, a currency discriminating apparatus is described, which utilizes the presence of a light-emitting substance in a printed zone of currency when irradiated with ultraviolet rays. The apparatus comprises an ultraviolet ray-emitting member, a photoelectric converter element, and a discriminating circuit for checking pattern signals.
Another illustrative approach discloses a counterfeit paper currency bill warning device that utilizes the characteristic fluorescence of genuine paper currency. In this device, an ultraviolet lamp illuminates the paper currency of unknown origin, and a sensor circuit responds to fluorescent radiation from the currency to give a signal to an indicator, which displays an indication of the fluorescence of the unknown paper currency relative to the fluorescence of genuine paper currency. The sensor is a photoresistor and the indicator is a variable intensity light or a digital display.